14 LABORATORY EQUIPMENT. 



Some part of the skin of the back is thoroughly disinfected and a well-fitting Bier cup 

 firmly applied. Suction arises and the skin assumes a dark bluish-red appearance. 

 After half a minute the cup is removed, the scarifier applied and the cutting edges set 

 free. The scarifier is then reapplied, but this time at right angles to the previous incisions 

 and the edges again set free. Suction is again made by the Bier cup and the blood is 

 thus forced out from the multiple incisions. 



FIG. 7. Obtaining blood by the wet cupping method. 



The blood obtained by any of the above methods is collected into a sterile 

 vessel (graduate, flask, test-tube) and allowed to coagulate. The clot is 

 then separated from the sides of the vessel by a sterile glass rod or platinum 

 needle, the vessel plugged with absorbent cotton and placed into the ice- 

 chest. After 12 to 24 hours the serum begins to separate out from the clot. 

 If the serum is required immediately, the blood is allowed to flow directly 

 into centrifuge tubes, the clot separated from the sides and the tubes centri- 

 fugalized. With a well regulated centrifuge serum appears after several 

 minutes. 



There are several rules to be kept in mind when using a centrifuge. 

 Rules for i. The machine must be well oiled. 



the Use of 2. The counterweights must be absolutely of the same weight. 

 Centrifuge. 3. The centrifuge should never be suddenly stopped, but allowed to do 



so of its own accord. 



4. In starting it, the motor should be gradually turned on. 



5. If the centrifuge is slightly out of order it should not be used, but repaired at once, 

 otherwise it may be ruined forever. 



6. One should never centrifugalize with cotton plugs in the test-tubes. If the latter 

 must be sealed, rubber stoppers should be used. 



